In most integrated circuit systems, it is necessary for a semiconductor chip (“on-chip”) to produce positive high voltage output (VP) and negative high voltage output (VN), the absolute values of which are higher than the input power source voltage (VDD). For example, in liquid crystal display driver apparati, in order to achieve high display quality, both positive and negative high voltage power sources and positive and negative high voltage driving voltages are needed when driving the liquid crystal screen. At this time, a charge pump comprising of one or more electronic switches, such as metal oxide semiconductors (MOS), and one or more coupling capacitors is used to raise an externally-provided voltage to the required high voltage.
FIG. 1 shows the structure of the current charge pump that produces a 2× increased voltage, including input voltage Vin; two electronic switches, S1 and S2, used for charging; two electronic switches, S3 and S4, used for discharging; a coupling capacitor C1; and an output capacitor Co.
FIG. 2 shows the control sequence for the four electronic switches used in the operation of this circuit. Herein, the control signal for electronic switches S1 and S2 and the control signal for electronic switches S3 and S4 do not overlap, and have Break Before Make (BBM) time. During time t1, electronic switches S1 and S2 are on, and electronic switches S3 and S4 are off; input voltage Vin charges capacitor C1; after capacitor C1 has stored a full charge, capacitor C1 stores a charge of value Vin. During time t2, electronic switches S3 and S4 are on, and electronic switches S1 and S2 are off; when input voltage Vin has gone through capacitor C1 to output terminal Vo, output terminal Vo then passes through output capacitor Co to the zero-potential voltage VSS line, and stores a charge with value 2Vin/(C1+Co) in output capacitor Co. Suppose C1=Co, without considering the power consumption of the electronic switches and capacitors; through repeated charging and discharging, a charge of value 2Vin can be stored in output capacitor Co, therby obtaining 2× voltage output, i.e. Vo=2Vin.
FIG. 3 shows the structure of the current charge pump that produces −1× increased voltage, including input voltage Vin; two electronic switches, S1 and S2, used for charging; two electronic switches, S3 and S4, used for discharging; a coupling capacitor C1; and an output capacitor Co.
Illustration 4 shows the control sequence for the four electronic switches used in the operation of this circuit. Herein, the control signal for electronic switches S1 and S2 and the control signal for electronic switches S3 and S4 do not overlap, and have BBM time. During time t1, electronic switches S1 and S2 are on, and electronic switches S3 and S4 are off; input voltage Vin charges capacitor C1; after capacitor C1 has stored a full charge, capacitor C1 stores a charge of value Vin. During time t2, electronic switches S3 and S4 are on, and electronic switches S1 and S2 are off; when input voltage Vin has gone through capacitor C1 to output terminal Vo, output terminal Vo then passes through output capacitor Co to the zero-potential voltage VSS line, and stores a charge with value (0−Vin)/(C1+Co) in output capacitor Co. Suppose C1=Co, without considering the power consumption of the electronic switches and capacitors; through repeated charging and discharging, −1× voltage can be obtained, i.e. Vo=−1Vin.
In current charge pump circuits, positive m-times voltage and negative n-times voltage must be simultaneously obtained, usually requiring (m+n−1) coupling capacitors, m≧2, n≧1, resulting in a rather large number of coupling capacitors in the charge pump. If the charge pump's coupling capacitors use on-chip capacitors, a large chip area is required, thereby increasing the cost of producing the circuit. If off-chip capacitors are used, the size and cost of the electronic equipment used to install the chip will also be increased. If a system requires multiple charge pumps, this problem only becomes more serious. Therefore, it is desirable to have a charge pump circuit that overcomes the problems of the prior art charge pump circuits.